您的代码看起来很正确,并且在我的小型测试应用程序中按预期工作。因此,我假设您在数据源方法中有一些错误。
这是我使用的:
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
return [[self.frc sections] count];
}
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
id <NSFetchedResultsSectionInfo> sectionInfo = [self.frc sections][section];
return [sectionInfo numberOfObjects];
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
CellView *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"CellView" forIndexPath:indexPath];
Item *item = [self.frc objectAtIndexPath:indexPath];
cell.name.text = item.name;
return cell;
}
-(UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
id <NSFetchedResultsSectionInfo> sectionInfo = [self.frc sections][indexPath.section];
Item *item = sectionInfo.objects[0];
Location *location = item.location;
HeaderView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader
withReuseIdentifier:@"HeaderView" forIndexPath:indexPath];
headerView.title.text = location.name;
return headerView;
}
获取的结果控制器创建如下:
- (NSFetchedResultsController *)frc
{
if (_frc == nil ) {
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Item"];
NSSortDescriptor *sort1 = [[NSSortDescriptor alloc] initWithKey:@"location.name" ascending:NO];
NSSortDescriptor *sort2 = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:NO];
NSArray *sortDescriptors = @[sort1, sort2];
[fetchRequest setSortDescriptors:sortDescriptors];
_frc = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:self.context
sectionNameKeyPath:@"location.name"
cacheName:nil];
NSError *error;
_frc.delegate = self;
[_frc performFetch:&error];
}
return _frc;
}
备注:带有获取结果控制器的集合视图的自动更新是相当棘手的,所以这篇文章
http://ashfurrow.com/blog/how-to-use-nsfetchedresultscontroller-with-uicollectionview
(带有代码示例)可能很有趣。